The goal of this research is better understanding of pulsatile blood flow in the mammalian circulation. Our experiments are intended to identify and measure the responses of smooth muscle in the arterial and venous trees to neurotransmitters and other vasoactive agents, and to investigate the consequences of physiologic control of large vessels as contrasted with the microcirculation. The mechanical responses of blood vessels will be studied in vitro, and the receptor populations of the vessels will be measured by radioligand methods. Correlation of the results of these two sets of data may clarify the mechanism of many vasomotor reactions that are now known only empirically. The potential clinical significance of the results lies in the central role of blood vessel regulation in certain disorders, such as hypertension and shock.